#include <stdio.h>
#include <string.h>

int main () {
  char str[] = "This is a string. нннн";
  char * pch;
  int count = 0;

  pch = strchr(str, 's');

  while (pch != NULL) {
    count++;
    pch = strchr(pch + 1, 's');
  }
  printf("%i", count);
  return 0;
}